Split feed naphtha reforming



Nov. 17, l97 J. MAzluK Erm.

SPLIT FEED NAPHTHA REFORMING Filed Aug. 1. 1968 e sheets-sheet 1 H .o lEomtw :O Q60 mv Qu mm Gm mm om o.. m

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Nov.'17, 1970 J. MAzluK ETAL 3,540,996

' SPLIT FEED NAPHTH'A REFOIRIMINGv Filed Aug. 1, 1968 e sheets-sheet zFIGB AROMATICS PRODUCTION AT ZOOPSIG FROM (Z6-350? MESA Split Feed vsConventional Reforming -C0nveniion0l Reforming -eSplif Feed Reforming 54w C* 53 5 l o5 E 52 5| e@ /nVen/ors John Maz/'alf 0000/0' A Zan o/n/ yf/ Lynl/L? Agent Nov. 17, 1970 J. MAznuK ETAL 3,540,996

. SPLIT FEED NAPHTHA REFORMING I Filed Aug. 1, 1968 6 Sheets-Sheet 5PRESSURE REFORMING CG- 400F KUWRIT FULL RANGE PARAFFINE NAPHTHA F lG.I[[ SPLIT FEED AGING BENEFITS IN LOW Days On Sream Split FeedConvenhonol o o suono 20110:; almmadwal 9| u| /m/en/Urs ./Ohn Maz/'ukDona/d A. Zano//n/ Nov. 17, 1970 J. MAzluK ETAL 3,540,996

SPLIT FEED NAPHTHA REFORMING n Filed Aug. 1, lesa s sheets-Shadi EFFECTOF SULFUR CONCENTRATION OF CATALYST PERFORMANCE Condition: ZOOPsig, IOLHSV, I4/I Total Gas/HC Recycle Ratio |02. (R+ 5) Raw Reormate OctaneNumber la.. Sulded 0.6% Pt Catalyst, Desiccafed Operation +|O 23 +5 "D 0f a 2 G 5 o lo l O "oe |o E $5 +5 E m w qu u O IOO 200 300 400 500 600700 800 Total Sulfur Entering Reformer,Weighr PPM of Naphfha /nl/enfO/,S

^ John Maz/'uk F G N A Dona] AZanQ//n/ Agent J. MAzluK ETAL 3,540,996

SPLIT FEED NAPHTHA REFORMING 6 Sheets-Sheet 5 V, l4/l Total Gas/ HCRecycle Ratio lO2.5( R+5) Raw Reformate Octane Number Sulfided 0.6

"/o Pt Catalyst, Desiccated Operation Nov. 17, 1970 Filed Aug. 1, 1968EFFECTOF SULFUR CONCENTRATION OF CATALYST PERFORMANCE Condition: ZOOPsig, LOLHS 500 Total SulfurEntering ReformerWeight PPM of Nophtha N O\om o lOO d lic 5 m o m. m. m w o w. m.. .w c o gmmoweoao 1Q E85@ O2 .NIQcoxe //7 V60/Org Jon/1 Maz/'uk Dona/0 A. Zano//n/ L 7J/'i Wm Agent FIGNB-Filed Aug. 1. 1968 FIGV J. MAzluK ErAL 3,540,996

SPLIT FEED NAPHTHA REFORMING' e sheets-sheet e U5. Cl. 20S-65 7 ClaimsABSTRACT F THE DISCLOSURE A method for improving the octane rating of apretreated full boiling range naphtha is defined to include reformingthe light naphtha portion thereof in an initial reforming processingregion and the heavy naphtha portion thereof in a final reformingprocessing region. The effluent from the initial reforming region ispassed with the heavy naphtha through the final reforming region and thetotal efiiuent is pressure fiash separated to permit recovery of ahydrogen rich recycle gas from a liquid reformate fraction which isstabilized to remove residual hydrogen and light hydrocarbons therefrom.The described process provides a lower catalyst deactivation rate,increased aromatics production and an improved front end octane rating.

BACKGROUND OF THE INVENTION The method and combination of processingsteps of the present invention is concerned with the catalytic reformingof a full boiling range naphtha fraction boiling in the range of fromabout C hydrocarbons up to about 400 F. so as to accomplish in thepresence of suitable hydrogenation-dehydrogenation reforming catalyst arelatively more selective dehydrogenation of naphthenes to thecorresponding aromatics, dehydrocyclization of paraflins to aromatics,isomerization and limited hydrocracking of some of the components of thenaphtha charge to the exclusion of increased coke formation. During anaphtha reforming operation, all of the above reactions are desirableand those reactions leading to the production of high octane materialssuch as aromatics are usually more desirable than the other reactions ofreforming.

It has been observed by those specializing in the catalytic reforming ofnaphthas that as the end boiling point of the naphtha is increased,there is a decided and significant tendency to increase coke formationrapidly when pushing to reach target octanes and such an increaseeffectively and undesirably limits the catalyst life of the process. Asa result of this, the prior art has developed different approaches toreforming; one process effects regeneration of the catalyst after ashort onstream period and the other adjusts the reforming process tomaintain catalyst life as long as possible before shutting down thereforming operation to regenerate the catalyst. The conventional orcurrent reforming practice involves the processing of naphtha through aseries of reaction zones wherein all of the naphtha processed is passedin series through each of the reaction zones. If a three reactor systemwere used to process a full range naphtha, at a given set of conditions,all of the naphtha would be processed in turn through each of the threereactors. It has been proposed to separate a naphtha charge into a highboiling and a low boiling fraction and to reform the fractionsseparately so that the lower boiling fraction may be subjected to eithermore severe or less severe reforming conditions than the higher boilingfraction. When reforming the lower boiling fraction under more severeconditions than the higher boiling fraction, it is possible to upgradethe lower boiling hydrocarbons to a greater extent so that the blended3,540,996 Patented Nov. 17, 19'70 reformates thereof combine to form agasoline of higher octane number than would be obtained if the fractionswere reformed together in the more conventional prior art manner.lHowever, reforming in this prior art spl1t feed manner has not beencompletely successful since the higher boiling fraction has most usuallybeen incompletely reformed. To offset this deficiency, it has beenproposed to subject the high boiling naphtha fraction to reforming underrelatively high pressure conditions but such a method of operation isknown to inhibit suitable conversion of paraffin constituents.

Another approach to the problem has been to separate the eiiiuentsobtained from reforming operations and to recycle certain fractions ofthe reforming stage for upgrading with fresh feed. However, it has beenobserved that in any one of the proposed combinations of split feedreforming operations disclosed in the prior art that they all containsignificant deficiencies which preclude obtaining a desired optimizationof desired reforming reactions. Generally, the proposed split feedoperations have been plagued with economic disadvantages which haveprecluded their commercial use to any significant extent.

An object of the present invention is to provide a processingcombination for reforming a full boiling range naphtha such as aparafiinic naphtha boiling in the range of C5 hydrocarbons up to about400 F under conditions which permit more selective optimization of thedesired reforming reactions including dehydrogenation of naphthenes,dehydrocyclization of paraffins and isomerization reactions, andpreferentially to modify those reactions contributing to the depositionof coke and formation of undesired gaseous constituents.

SUMMARY OF THE INVENTION The present invention is concerned withreforming a naphtha boiling in the range of from about C5 hydrocarbonsup to about 400 F. which has been treated by hydrogenation to removesulfur and nitrogen constituents from at least the lower boilingportions thereof to a desired low level. That is, desulfurization anddenitrogenation of the naphtha charge is effected so that at least thelower boiling portion of the naphtha boiling below about 290 F. willcontain less than about l p.p.m. 0f either sulfur or nitrogen therein.The full boiling range naphtha charge is separated such as by splittingor fractionation into a light naphtha fraction and a heavy naphthafraction at a cut point selected from within the range of from about 250F. to about 290 F. Desulfurization and denitrogenation of the lowboiling naphtha fraction may be accomplished after splitting the naphthaas recited herein. The light naphtha fraction thus obtained or selectedis mixed with a hydrogen rich recycle gas stream which is substantiallyfree of innocuous concentrations of sulfur and nitrogen constituents sothat when combined with the light naphtha the mixture will contain lessthan about l p.p.m. of sulfur or nitrogen. The light .naphtha-hydrogengas mixture is also adjusted to provide a moisture level in the range of5 to about 15 p.p.m. of water in the initial portion of the lightnaphtha processing region or section of the present invention. The lightnaphtha reforming section is formed by at least two sequentiallyarranged reaction zones provided with suitable heaters and heat exchangemeans in conjunction therewith for heating the light naphtha chargeeither alone or in combination with hydrogen to a desired elevatedreforming temperature. The heated light naphthahydrogen mixture is thenpassed in contact with a platinum group metal reforming catalystdisposed in the sequentially arranged reaction zones comprising a firstpartial catalyst fill reaction zone followed by a full fill catalystreaction zone. For example, the initial reforming zone first contactedby the light naphtha will contain only a portion of the reformingcatalyst to be contacted by the naphtha and thus is referred to as apartial fill reaction Zone which may contain half or less than abouthalf of the amount of catalyst employed in the second or full fillreaction Zone. In this combination of catalyst reaction zones, the lowboiling naphtha fraction is initially selectively reformed in thepartial catalyst fill reaction zone under conditions selected tooptimize the dehydrogenation of naphthenes and thereafter the reformingconditions are adjusted for the full catalyst fill reaction Zone so asto effect primarily dehydrocyclization of paraffins and isomerizationreactions therein. YAs described herein, heating means are providedupstream of the reaction zones for adjusting the temperature of thereactant streams as desired before being introduced to a reaction zone.Thus, the efliuent obtained from the first catalyst reaction zone istemperature adjusted prior to the effluent being passed in contact withthe catalyst in the second or full fill reaction zone. The heavy orhigher boiling portion of the naphtha charge boiling above about 250 or290 F. is reformed in the presence of the reformate of the light naphthareforming operation and a catalyst aging inhibitor such as, for example,a sulfur compound such as thiophene. The higher boiling portion of thenaphtha charge containing a sulfur inhibitor in an amount of from about150 p.p.m. to about 350 p.p.m. and combined with the total hydrogen richeffluent of the low boiling naphtha reforming operation is heated to asuitable reforming temperature and then reformed in a final reformingprocessing region. The final reforming processing region is formed of atleast two sequentially arranged reaction zones, the first of whichcontains a smaller volume of catalyst than the latter. In these catalystreforming zones, the reforming conditions are particularly selected forreforming the higher boiling hydrocarbon constituents found in thenaphtha fraction boiling above about 250 F.290 F. In this finalprocessing region, the high boiling naphtha fraction passes sequentiallythrough the two reaction zones, the first of which contains lessplatinum reforming catalyst than the subsequent and first reformingzone. Thus, the naphtha charge comprising the high boiling naphthasequentially contacts a partial fill of reforming catalyst followed by asecond reactor containing a full fill of reforming catalyst. In thiscombination the amount of catalyst in the partial fill reaction zone maybe about one half of the amount of catalyst employed in the full fillreaction zone. Suitable means are provided for adjusting the temperatureof the hydrocarbon stream to a suitable reforming temperature beforeintroduction to each reforming zone.

In the combination of processing steps above described comprising theinitial and final reforming processing regions, hydrogen rich gasgenerated in the process is caused to move sequentially through acombination of reaction zones wherein the first and third reaction zonescontain less than and only about one half of the catalyst employed inthe second and fourth reaction Zones. By this arrangement of processingsteps the reforming severity conditions for each of the low boiling andhigh boiling naphtha fractions can be more selective for reforming thehydrocarbon components found therein and when required the severityconditions for reforming the low boiling naphtha fraction can be moresevere than required for the higher boiling naphtha. The hydrogen richgas employed includes recycle hydrogen gas in combination with thehydrogen produced during reforming thel light naphtha fraction in thefirst and second reaction zones and provides the hydrogen requirementsfor the high boiling naphtha fraction reformed in the third and fourthreaction zones. 'I'he hydrogen concentration of the efiiuent obtainedfrom the initial processing region comprising recycle and generatedhydrogen may be adequate in one embodiment for furnishing the hydrogenrequirements of the final processing region thereby contributingsignificantly to the overall economic advantage of the process. In yetanother embodiment, a portion of the hydrogen rich recycle gas may berecycled directly to the high boiling naphtha reforming step. Thushydrogen recycle gas may be passed in parallel flow arrangement to eachreforming stage. The effluent recovered from the last reaction zone ofthe final processing region is then separated to recover a hydrogen-richrecycle gas drawn from a liquid reformate eiiuent stream, Thisseparation may be accomplished by an initial pressure ash separation soas to recover a relatively high pressure recycle gas from a liquidreformate product. The liquid reformate product thus separated fromhydrogen containing gaseous constituents is further separated in asuitable stabilizer tower maintained under conditions to effect theseparation and recovery of any residual hydrogen and light hydrocarbonsseparated from a desired liquid reformate product.

The separated hydrogen containing gas is purified in a gas purifier forthe removal of undesired sulfur and nitrogen compounds, combined halogenand Water, when found, from the recycle gas thereby providing a recyclegas enriched in hydrogen. The recycle gas purifier may be substantiallyany suitable gas purifier for accomplishing the above purpose. In themethod of the present invention a molecular sieve gas purifier may beemployed for this purpose. When using a molecular sieve gas purifier, itis preferred that at least two molecular sieve gas purifiers be employedin parallel arrangement so that while one is being regenerated, theother may be onstream removing undesired gaseous components from thehydrogen recycle gas employed in the process. Hydrogen rich gas thuspurified is recycled in a desired quantity for admixture with the lightnaphtha fraction passed to the first reactor in the initial processingregion. In cooperation with the processing steps above identified,selective reforming of the low boiling naphtha fraction is enhanced bycontrolling thc moisture content of the combined hydrogennaphtha chargepassed in contact with the initial reforming catalyst. Thus, provisionsare made for adding a desired and controlled amount of water to therecycle gas and/or naphtha charge prior to the mixture coming in contactwith the catalyst in the first reactor of the initial reforming region.

The catalysts which may be employed in the reactors of the initialreforming region and the reactors of the final reforming region areknown generally as platinum group metal reforming catalysts and may be acombination of several different ingredients which will be helpful tothe selective operation herein discussed. Typical of the platinum groupmetal reforming catalysts which may be successfully used are catalystscomprising from about 0.l to about 2 percent by weight of platinum,preferably from about 0.35 to about 0.6 percent platinum alone or incombination with from about 0.1 to about 0.8 percent by weight ofhalogen dispersed in a suitable support material comprising an aluminasupport material. The alumina may be promoted with silica, glycerine,boron and combinations thereof and other activating ingredientscontributing to provide a desired cracking activity to the catalyst.

The present invention contemplates and provides for reforming a fullboiling range paraffinic naphtha at a reforming pressure below about 600p.s.i.g. and preferably at a pressure in the range of from about toabout 500 p.s.i.g. in the presence of a particle form platinum groupmetal reforming catalyst. Reforming of the low boiling naphtha fractionis generally effected in the presence of a controlled amount of waterbut in the substantial absence of any sulfur and nitrogen compoundswhich are preferably maintained at least below about 10 p.p.m. Thehigher boiling naphtha fraction on the other hand is reformed in thepresence of a substantial amount of sulfur either added or present inthe high boiling portion of the naphtha feed so that amounts greaterthan about 50 p.p.m. and preferably at least about 350 p.p.m. but notmore than about 1000 p.p.m. of sulfur is provided. In the particularcombination of this invention, the hydrogen to naphtha mole ratio ismaintained in the range of from about 4 to about 20:1 and preferablyfrom about 8 to about 14:1 While employing a space velocity in the rangeof from about 1 to about 20 and preferably from about 1 to about 3volumes of naphtha per hour per volume of catalyst. The temperatureemployed in each of the reforming Zones is selected to optimize thereactions to be eifected therein and these temperatures will bedependent in part upon the activity of the catalyst employed and thatrequired to produce a particular C5| octane product. Generally thetemperatures employed will be in the range of from about 800 to about1000 F. and preferably from about 850 to about 980 F.

The full boiling range naphthas employed in the development leading upto the present invention are identified in the following Tables 1through 4. These tables are selfserving and elaboration thereon is notfound necessary.

TABLE l Properties of light parainic naphtha (C6-290 F, Aramco)Distillation, ASTM F.:

IBP 152 5% vol. 180 10% vol. 185 vol. 190 vol. 198 vol. 207 vol. 215vol. 225 70% vol. 236 80% vol. 247 90% vol. 260 EP. 283

Specific gravity .7128 Molecular weight 102 Octane rating (R4-3) 70Composition, wt. percent:

Parans 73.9 Naphthenes 17.2 Aromatics 8.9

TABLE 2 Properties of heavy parat-linie naphtha (290-350" F. Aramco)Distillation, ASTM F.:

IBP 287 5% vol. 295 10% vol. 296 20% vol. 298 30% vol. 300 40% vol. 30350% vol. 306 60% vol. 310 70% vol. 314 80% vol. 320 90% vol. 330

Specic gravity .7653 Molecular Weight 133 Octane rating (R4-3) 60.5

Composition, wt. percent:

Parains 58.6 Naphthenes 21.4 Aromatics 200 6 TABLE 3 Properties of widerange naphthenic naphtha (Cs-350 F. Mesa) Distillation, ASTM F.:

IBP 169 5% vol. 197 10% vol. 204 20% vol. 214 30% vol. 224 40% vol. 23550% vol. 246 60% vol. 261 70% vol. 279 vol. 297 vol. 321

E.P. Y 352 Specific gravity .7632 Molecular weight 109 Composition, wt.percent:

Parains 41.2 Naphthenes 3 5 .1 Aromatics 23.7

TABLE 4 Properties of full range parainic naphtha (C6-400 F. Kuwait)Distillation, ASTM F.:

IBP 166 5% vol. 209 10% vol. 221 20% vol. 235 30% vol. 249 40% vol 26850% vol. 289 60% vol. 309 70% vol. 332 80% vol. 351 90% vol. 371 E.P.401 Specific gravity .7455 Molecular weight Octane rating (R-I-3) 64Composition, wt. percent:

Parains 65.2 Naphthenes 20.7 Aromatics 14.1

DESCRIPTION OF SPECIFIC EXAMPLES Studies were made employing the splitfeed technique of this invention with a paraflinic as well as amoderately naphthenic wide boiling range naphtha. The initialinvestigation involved a series of yield-octane surveys processing C6350F. Mesa naphtha split at about the 290 F. cut point employing a threereactor system maintained at an operating pressure of about 200 p.s.i.g.Light naphtha (C6-290 F.) was fed into the first reactor and theremaining heavy portion (29o-350 F.) was mixed with the processed lightnaphtha emerging from the secon-d reactor and the resulting mixture wasthen processed in th third reactor. In one yield-octane survey, acatalyst aging inhibitor was mixed with the heavy naphtha prior toprocessing as described above.

Results obtained with processing the Mesa naphtha leads to the followingconclusions:

(1) The use of a sulfur compound such as thiophene as a catalyst aginginhibitor added to the heavy naphtha 7 has no significant detrimentaleffect on overall yields or product distribution.

(2) Split feed yields (C6-F, 05+, hydrogen purity and hydrogenproduction) were slightly lower than those obtained by conventional 200p.s.i.g. operation.

(3) Split feed reforming produces a higher concentration of aromatics inthe C6+ reformate which results in a higher aromatics production basedon charge.

(4) Split feed reformates produced by present invention show significantimprovement in front end octane number.

(5) No apparent catalyst aging was observed over the test period.

A second run was made using the split feed technique with the primaryobjective of determining the aging characteristics of a platinum groupmetal reforming catalyst when processing a Ces-400 F. Kuwait naphtha at200 p.s.i.g. in a four reactor reforming system at a severity of 102 rawleaded octane. The full range naphtha was split at about the 290 F.boiling point and the heavy portion of the naphtha was dosed with acatalyst aging inhibitor thiophene to obtain 300 p.p.m. sulfurconcentration therein. This heavy naphtha fraction was processed in onlythe last two reactors of the four reactor system. When compared withconventional 200 p.s.i.g. reforming without splitting the feed, the dataobtained permit the following conclusions to be drawn.

(l) Split feed processing as dened by this invention has resulted in adrastic reduction in catalyst aging. Where conventional reforming showsabout a one month catalyst life before reaching a 980 F. inlettemperature, split feed reforming practiced according to this inventionwill at least double the length of the catalyst life.

(2) A signicant improvement in the front end octane number has ybeenobtained.

(3) Overall product yields are lower than those obtained by conventional200 p.s.i.g. operation (Table 5) but are considerably higher thanestimated for a higher pressure operation which would be required tocompensate for the aging normally observed at low pressure.

(4) When based on reformer charge, split feed reforming practicedaccording to this invention produces a higher yield of C6+ aromatics(Table 5).

(5 On a distribution octane number (DON) basis, the split feed reformingoperation of this invention shows liquid yields comparable to thoseobtained with conventional reformer operation in conjunction with asignificant improvement in C6+ aromatics production (Table 6).

TABLE 5.-A COMPARISON OF YIELDS OBTAINED ON FULL RANGE PARAFFINICCri-400 I". KUWAIT NAPHTHA AT 102.5 C-i- (Ri-3) O.N. SPLIT FEED VS.CONVENTIONAL REFORMING C-l- (R+3) O.N 102.9 102.5

A A Split S.F.- Split S.F. feed Conv. conv. feed Conv. conv.

C54-, Vol. of chg- 68. 9 7l. 4 -2. 5 68. 2 71.1 2. 9 05+, vol. of chg-75. 7 78. 4 2. 7 75. 6 78. 2 3. 9 05's, Vol. of chg 6.8 7. 0 0. 2 7. 47.1 +0. 3 C4s, vol. oi chg 6. 7 6. 2 +0. 5 6. 9 6. 2 +0. 7 C3, wt.percent of chg 4. 6 4. 4 -l-O. 2 4. 7 4. 2 +0. 5 C2, wt. percent of chg3. 6 3. 4 +0. 2 3. 7 3. 5 +0. 2 C1, wt. percent oi chg 2. 2 1. 9 +0. 32. 4 2. 0 +0. 4

Ce|-, (R+3) O.N 102.5

A Split Conv. S.F.. feed ref conv- Ce-I- yield, vol. percent chg 68. 471. 4 -3. 0 Cs-laromatics, vol. percent chg 43. 1 41. 6 +1. 5 Cia-{-Paraflns, vol. percent chg 19. 2 23. 8 -4. 6 C-laromatics, vol. percentof Ca-iref 63. 58. 2 +4. 8 Ca-I- Parans, vol. percent of ref- 28.1 33. 3-5. 2 103. 6 Base +3. 6

Vol. percent of aromatics prod TABLE 6.-A COMPARISON OF YIELDS OBTAINEDON FULL RANGE PARAFFINIC (9e-400 F. KUWAIT NAPHTHA ON A DON (R4-3) BASISSPLIT FEED VS. CONVENTIONAL REFORMING Raw reformate (DON+3) O.N 100.7

A Split Conv S.F. fee r conv C64-(R473) O.N 103. 5 Cel-liqu1d yield,vol. percent chg .2 68. 5 -0. 3 Cyl-liquid yield, vol. percent chg-- 75.6 75. 9 0. 3 Ce-lproduct:

Aromatics, vol. percent oi Ciriref 63. 0 60. 5 +2. 5 Parailns, vol.percent of Ca-lref 28. 1 30. 5 -2. 4 Aromatics, vol. percent of chg 42.8 41. 4 +1. 4 Parafns, vol. percent of chg 19. l 20. 9 -1. 8

In order to further identify the advantages accruing from the method andarrangement of processing steps of this invention, data developed andrecorded during the investigation are graphically recorded forconvenience of illustration.

FIG. I shows in graphical form the effect of continuous sulfur additionon the stability of a reforming catalyst of low platinum content whenprocessing a heavy 290-350 F. Aramco naphtha at low pressure of about200 p.s.i.g. The data are self serving and show that the stability ofthe catalyst (minimized rise in inlet temperature required for octaneproduction over the operating period) was vastly improved when theamount of sulfur in the charge was increased from 3 to 150 ppm. andimproved even further when the sulfur level was increased to 310 p.p.m.

FIG. II graphically shows the aromatics production at 200 p.s.i.g. whenemploying the split feed method of this invention as compared with thatobtained by the conventional prior art method above described. Thesedata clearly illustrate the significant improvement in C6+ aromaticyield obtained by the method of this invention.

FIG. III, on the other hand, graphically shows the catalyst agingbenefits obtained by a split feed operation of the present inventionover the conventional operation. In the conventional operation thecatalyst ages much more rapidly and requires a much more frequent'regeneration cycle than the split feed operation of this invention.

FIG. IV provides graphically a group of curves which shows how sulfuraddition affects product distribution when processing a light parainicnaphtha (C6-290 F.) Aramco at 200 p.s.i.g. It is observed from thesedata that sulfur has an undersirable effect on the light naphthafraction by causing a detrimental yield shift to lower C6+ liquid and H2yields while increasing the amounts of C5 and light hydrocarbons.

FIG. V presents diagrammatically in elevation an arrangement ofinterconnected Vessels for practicing the method and concept of thepresent invention.

Referring now to FIG. V by way of example there is shown a pretreatednaphtha charge substantially freed of undesired nitrogen and sulfurconstituents and boiling in the range of from about C5 to about 400 F.being introduced to the split feed processing scheme of this inventionby way of conduit 2 communicating with splitter tower 4. In splittertower 4, the naphtha charge is separated into an overhead low boilingnaphtha fraction or light naphtha boiling in the range of from about C5hydrocarbons up to about 290 F. and a higher boiling bottoms or heavynaphtha fraction boiling from about 290 F. up to about 400 F. iIt iswithin the scope of this invention however to make the rough cut pointbetween the low and high boiling naphtha fraction of some other boilingpoint and the cut point may be as low as about 250 F. depending upon thecomposition of the naphtha charge being processed. In the arrangementshown, the low boiling naphtha fraction is withdrawn from the upperportion of splitter 4 by conduit 6 com- 9 municating with heater 8. Inheater 8 the light naphtha charge recovered from splitter 4 is combinedwith hydrogen rich recycle gas obtained as hereinafter described andheated to an elevated temperature suitable for introduction to theinitial reforming region reactor 12 by conduit 10. Reactor 12,containing a suitable platinum reforming catalyst known in the art anddescribed herein is diagrammatically shown as about half the size of thesecond downstream reactor 20. The reactors may -be of the same size andthe first reactor only partially filled with reforming catalyst ashereinbefore discussed so that it contains only about one half of theamount of catalyst employed in the second reactor. In reactor 12, thelight naphtha is subjected to reforming conditions selected to obtaindesired naphthene dehydrogenation and thus partial reforming of lightnaphtha constituents most easily convertible to aromatics. The totaleffluent of reactor 12 is withdrawn and passed by conduit 14 to heater16. In heater 16, the effluent of reactor 12 is reheated to a desiredelevated reforming temperature and the reheated efliuent is then passedby conduit 18 to a second full fill platinum catalyst reactor 20. Inreactor 20, the partially reformed light naphtha charge is furtherreformed under relatively more severe conditions selected to effectdehydrocyclization and isomerization reactions to desired productmaterial without significant hydrocracking. The efliuent of reactor 20is withdrawn by conduit 22 communicating with conduit 24. The heavy orhigh boiling portion of the naphtha charge obtained in splitter 4 isremoved therefrom by conduit 24. In conduit 24 the heavy naphtha may bemixed with the total light naphtha efiiuent of reactor 20 and themixture then passed to heater 26 or the light naphtha effluent which isat an elevated temperature may be mixed with heavy naphtha feed afterheating the heavy naphtha either alone or in the presence of hydrogenrich recycle gas. In heater 26 the naphtha charge comprising the heavynaphtha either with or without the light naphtha effluent and recyclehydrogen is heated to a suitable elevated reforming temperature selectedfor reforming primarily the heavy components of the naphtha charge whichare most easily convertible to aromatic constituents. The heated chargeis then passed by conduit 28 to reactor 30 after the addition of thecatalyst inhibitor as herein described. Reactor 30, similarly to reactor12, contains only about one half of the volume of catalyst as employedin a second downstream reactor and thus is shown diagrammatically to beonly about one half the size of the downstream reactor. Reactor 30,similarly to reactor 12, may be the same size as the other reactor butonly half filled with active catalyst as discussed hereinbefore. Asulfur compound catalyst inhibitor such as thiophene and supplied byconduit 32 is added to the heated naphtha-hydrogen mixture in conduit 28being passed to the reactor 30. In reactor 30 the reforming conditionsare selected which are most suitable for converting naphthenes toaromatics. The effluent of reactor 30 is then passed by conduit 34 toheater 36 wherein the naphthahydrogen effluent is reheated to a suitableelevated reforming temperature to achieve further selective reforming inreactor 40 of the high boiling constituents of the naphtha charge toaromatics and isomerization products contributing to a desired highoctane product. As noted above, reforming of the naphtha charge iscompleted in the full fill catalyst reactor such as represented byreactor 40. In reactor 40, the naphtha-hydrogen mixture is contactedwith a suitable platinum reforming catalyst under those conditions mostselective to complete dehydrocyclization and isomerization of the higherboiling components of the naphtha charge without experiencing undesiredhydrocracking reactions therein. The total reformate product of theselective reforming steps above discussed is then passed by conduit 42to a high pressure separator 44 for separating a hydrogen containing gasstream from a liquid reformate product stream. The

effluent in conduit 42 may be partially cooled before being passed toseparator 44. A hydrogen containing gas stream is removed from the upperportion of separator 44 by conduit 46 and passed to recycle gas purifier48.

In recycle gas purifier 48, the hydrogen containing recycle gas istreated with, for example, a solid adsorbent material such as amolecular sieve material under conditions to remove low boilinghydrocarbons, sulfur and nitrogen compounds as well as water andcombined halogen compounds found in the recycle gas stream. It is to beunderstood that two recycle purifiers 48 may be employed in parallelflow arrangement with one anothenso that while one gas purifier is beingregenerated, the other may be concurrently employed to treat hydrogencontaining recycle gas as discussed above. The gas thus treated andthereby enriched in hydrogen is removed by conduit 50 and recycled foradmixture with the light` naphtha fraction in conduit 6 before passageto heater.

8. Provision is made for withdrawing a portion of the enriched hydrogenrecycle gas by conduit 52 and provisions are also made for adjusting themoisture content of the hydrogen rich recycle gas by conduit 54 providedfor introducing water thereto or into the naphtha charge. The liquidreformate product separated in 44 is withdrawn from the bottom thereofby conduit 56 and passed to a stabilizer tower 5'8. In stabilizer towerS8, conditions are maintained to permit the recovery of LPG gaseousconstituents from the upper portion thereof by conduit 60 and astabilized liquid reformate product from the lower portion thereof byconduit 62. It is to be understood that the processing arrangement abovediscussed may be varied by the inclusion of pumps and valves, not shown,but is intended to be limited to the particular combination and sequenceof steps generally described with respect thereto. It is also to beunderstood that the operating temperature conditions may be varieddepending upon the type of naphtha being processed and the catalystcycle life without departing from the processing combination intended tobe covered by applicants invention.

We claim:

1. A method for reforming a naphtha charge comprising portions boilingabove and below about 290 F. which comprises passing a portion of thenaphtha charge boiling below about 290 F. which has been pretreated toobtain a low level of sulfur with hydrogen rich recycle gas sequentiallythrough a plurality of reforming reaction zones arranged to have avolume of platinum containing catalyst in the first and third reactionzones substantially the same but the volume of catalyst in either zonebeing less than the volume of catalyst maintained in each of the secondand fourth reaction zones, maintaining the reforming reaction conditionsin the first and second reaction zones more severe than in the remainingreaction zones, reforming the naphtha portion boiling above about 290 F.in the presence of from about 150 to about 1000 p.p.m. of sulfur in thethird and fourth reaction zones, separating an effluent recovered fromthe last of the reforming zones to recover a stabilized liquid reformateproduct and a hydrogen rich gas containing less than about 5 p.p.m. ofsulfur and recycling the hydrogen rich gas to the first reaction zoneunder conditions to pro.- vide from about 5 to about 15 p.p.m. ofmoisture in the charge thereto.

2. The method of claim 1 wherein said low boiling portion is reformedunder conditions of moisture control to inuence the dehydrogenation ofnaphthenes in a substantial amount prior to effecting substantialdehydrocyclization and isomerization of hydrocarbon constituents in thelow boiling portion, reforming the high boiling naphtha portion in thepresence of the total effluent obtained by the above recited low boilingnaphtha reforming operation in the presence of a substantial amount ofsulfur so as to inuence dehydrogenation, dehydrocyclization andisomerization of hydrocarbon components in the high boiling naphthaportion with a platinum reforming catalyst. v

3. The method of claim 1 wherein the catalyst employed to reform the lowboiling naphtha portion contains about 0.35% by weight of platinum andthe catalyst employed to reform the high boiling naphtha fractioncontains about 0.6% by weight of platinum.

4. The method of claim 1 `wherein the sulfur content of the chargecomprising the low boiling naphtha fraction is less than 10 p.p.m. ofsulfur.

5. The method of claim 1 wherein the sulfur content of the low boilingnaphtha is maintained below about 5 p.p.m. and at least about 350 p.p.m.in the high boiling naphtha. fraction.

6. The method of claim 1 wherein all of the hydrogen requirements of thehigh boiling naphtha reforming operation are provided by the efuent ofthe low boiling naphtha reforming operation.

7. The method of claim 1 wherein reforming of the References CitedUNITED STATES PATENTS 2,901,415 8/1959 Hemminger et al. 208-65 2,990,3637/1961 Evans 208-65 2,946,737 7/ 1960 Potas 208-65 3,242,066 3/ 1966Myers 208-138 3,347,777 10/ 1967 Davis 208-65 HERBERT LEVINE, PrimaryExaminer U.S. C1. X.R.

